Process of manufacturing artificial silk and the like



Patented Nov. 19, 1928 HARRY 1P. BASSETT, OF CYNTHIANA, KENTUCKY, AND THOMAS E. BANIGAN, OF CLIFTON HEIGHTS, PENNSYLVANIA, ASSIGNORS, BY MESHE ASSIGNMENTS, T0 SAID BASSETT rnocnss OF MANUFACTURING ARTIFICIAL SILK AND THE LIKE No Drawing. Application filed May 19,

This invention relates to the manufacture of artificial silk, horsehair, straw, and sim-' other non-cellulose constituents of the plant fibre from which the cellulose is obtained and the cellulose obtained essentially in a pure state. It has been found that cellulose exists in three forms, namely, the alpha, beta, and gamma. Of these forms, only the alpha cellulose is useful in the preparation of artificial silk and similar fibres and films, while the beta and gamma cellulose, if present withthe alpha cellulose, simply serve to dilute and 1n ure the quality of the artificial fibre without adding an additional strength.

t has been customary heretofore 1n purl fying cellulose from plant fibres to remove the gums, resins, lignin, beta cellulose, gamma cellulose and other impurities by boilinglor steeping with solutions of caustic alkalies, or this procedure followed by drastic treatment with bleaching agents. In the course of our investigations, we have studied the action of these treatments on various fibres such as cotton, hemp, jute, flax, etc., and have found that such ,treatment is injurious to the strength, purity, and yield of the resulting cellulose. Cellulose so prepared usually contains a considerable amount of beta cellulose as well as decomposition products produced by the hydrolytic action of caustic alkalie's employed during considerable perlods of time at high temperature.

These impurities while somewhat similar to alpha cellulose in their behav or-toward solvents for cellulose, when present in finished silk or similar products, act practically as inert material, thereby rendering the product harsher, less uniform, weaker, and of less permanent stability than when essentially pure alpha cellulose is employed.

We have discovered that when cellulosebearing plant fibres such as cotton, flax, hemp, and ramie are subjected to a prelimlnary acid 1924. Serial No. 714,497.

treatment, in the manner described in the patent to Harry P. Bassett, granted January 3, 1922, No. 1,402,040, for a short period of time, followed bya suitable alkali boiling or steeping treatment, the resulting cellulose consists essentially of pure alpha cellulose of such purity that it is suitable for the production of very high quality artificial silk, horsehair, straw, films, and similar products; and

that artificial silkmade from such cellulose has remarkable strength, lustre, loftiness, and stability' due to the absence of inert impurities.

lVe have discovered also that by proper preliminary acid treatment followed by an alkali. treatment, the viscosity of the cellulose solution can be controlled between such wide limits .thatgreat flexibility is possible in the size and softness of fibres or filaments spun from a solution of such cellulose. It has been possible with cellulose prepared in this manner to spin fibres'ranging from one denier to artificial horse-hair of 300 to 600 deniers.

It is customary in present processes for manufacture of artificial silk by the cuprammonium process to spin the silk onto rolls or spools and to wash and bleach on these rolls.

It is customary also to dry the silk on these or similar rolls or reels on which the silk attains essentially its complete drying. As the silk drys, it shrinks greatly, and as it is obliged to dry on a rigid cylinder, the silk fibres are placed under extreme tension which is so near the elastic limit of the fibres that many of the fibres break and the texture of the silk is rendered comparatively stiff and harsh.

We have discovered that cuprammonium silk can be spun on rolls or reels on which the silk can be given a superficial washing to remove the main portion of the alkali and copper in the fibre, and that the silk can then be removed from the roll or reel, twisted while wet, and reeled into hanks, in which form the silk can be given its final washing and bleaching treatments and can then be dried in the hank, without being held under tension, to its final dryness and then wound on spools ready for use with very satisfactory results. We have found that somewhat better results can be obtained by giving the Wet silk in hank form its initial drying to a moisture content of 30 to 40 per cent, after which it is wound acid, that it is practically impossible to re-.

move the last traces of the mineral acid emstrength of the finished product.

ployed. These final traces of mineral acid appear to exist partly as unstable acid compounds of cellulose as, for example, cellulose sulfate. These compounds gradually decompose in the finished product, resulting in gradual deterioration of the color and Wehave found that the final traces of copper and alkali can'be removed from freshlyspun cuprammonium silk by organic acids, preferably acetic acid without formation of traces of acid-cellulose compounds and with no deteriorating effect on the silk. We have found that even when traces of acetic acid are left in the silk that the silk can be dried with q no injurious effect.

In practicing the process formingthe subject matter of the present invention, the base material used for manufacturing the silk is.

preferably purified cellulose, derived from plant fibres such as cotton, wood pulp, flax,

emp, ramie, et-c., but we prefer to use cotton, particularly the variety known as secondcut linters.- In the preferred method, the

. cotton is treated as in the manner described in Patent No. 1,402,040, granted to Harry P. Bassett on January 3, 1922, by boiling with dilute acid as, for example, sulfuric acid of a strength of from 0.10 per cent to 0.24 per cent in water for about one hour, followed by boiling in dilute alkali, preferably sodium hydroxide of a strength equal to 5 to 6 pounds of alkali per 100 pounds of dry cotton'for about 4 hours. The cellulose is then washed and wholly or partially freed from water.

The cellulose is then dissolved in a mixture of copper hydroxide and ammonium hydrox ide. Considerable variation is possible in the roportion of copper hydroxideto cellulose ut, we generally use about 3 parts-of copper hydroxide to 4 parts of dry cellulose, though this proportion may vary from about 1 part of copper hydroxide to 2 parts of cellulose to equal parts'of each. Considerable variation can be made in the strength of ammonium hydroxide used,'but in eneral we prefer to use ammonium hydroxiife ofabout 20 to 26 Beaum.

- When dissolving cellulose for manufacture of artificial silk of extreme softness and finer hydroxide in 100 cc. of ammonium hydroxide of 20 to 26 Beaum. \Vhen it is desired to make silk of 80 to 175 deniers, we prefer to dissolve 6 to 10 grams of purified cellulose to each 100 cc; of ammonium hydroxide.

The spinning solution so prepared is then filtered to'remove particles of foreign matter and any undissolved copper compounds.

The-method of spinning consists in forcing the spinning solution by low air pressure from a supply tank to the spinnerets through whichit -is extruded intov the precipitating bath surrounding the tips of the spinnerets wherebythe solution is solidified into fibres. The spinnerets may consist of a suitable number of orifices 0r jets arranged in small clusters to furnish a silk thread of the desired number of fibres which are together passed through a guide and from that onto a roll or.

reel rotating in a bath which consists of exactly or approximately the same composition as the precipitating solution. The precipitating solution may consist of a solution of sodium or potassium hydroxides or a mixture of the two, but preferably is a solution of sodium'hydroxide of a concentration equivalent to 30 to 50 Beaum. As most of the ammonia used in the spinning solution dissolves in the precipitating: solution, it is necessary'constantly to remove part of the solution and recover its ammonia content, replacing in the spinning bath an equal supply of fresh solution.

After a suitableamount of silk has 'been wound onto the roll or reel, termed the spinning cylinder, the cylinder is removed, centrifuged, or. rotated rapidly for a few seconds to remove the excess of strong alkali soaked for a fewminutes in water or weak sodium hydroxide solution; is again centrifuged for a few seconds to remove most of the adhering-solution; and then removed to a twisting machine. The threads are iven the proper twist and are then reeled 0 into hanks.

In place of the stationary spinnerets, we I alkali. This operation is done by progressive extraction in a series of. tanks in such a we that the copper and alkali content of the wash waters is built up so asto be economically recoverable. For example, the liquor used as the first washing of a batch of hanks may be strong enough to be sent directly to the resecond Washing for this batch of hanks may be used as the'first washing liquor for the next successive batch of hanks. Or, several batches-of hanks maybe given their first washing in a certain liquor before it is necessary that the liquor be'sent to'therecovery system. I 1

After the silk has been practically freed of soluble alkali and copper, it is soaked for a short time in a dilute solution of an organic acid, preferablyacetic acid,which removes the last traces of alkali, copper, and iron.

The silk is then washed free of the last traces of copper and alkali salts by progressive washings by the same method as employ-' ed for removal of sodium hydroxide. When the acidsolution containing copper and sow dium acetate or sodium salt of the organic acid used is built up to an economic strength for recovery, the acid liquor is transferred to the recovery system.

If it is desired to produce bleached silk, the washedsilk, may next be given 'a bleaching treatment in an alkaline bleach of a strength not in excess, of the-equivalent of 6 pounds of lime bleach per 100'p'ounds of dry silk at v a temperature not in excess of 120 F. for a short periodof time, usually less than 1 hour,

after which the hanks are removed from the bleach solution and immediately placed in a tank of Water very. slightly acidified with acetic or other organic acid, at ordinary temperature, for about 10 minutes. Theihanks are then washed thoroughly in fresh water.

The ban s of silk are then hung in a dryer in which t e humidity can be controlled and the silk may be gradually dried down to a moisture content of 7 .per cent. It is necessary that humidity be carefully controlled during, particularly, the earlier stages of drying so that the threads on the inside and on the outside of the hank may dry essentially at a the same rate. Unless this condition is controlled, there results a tendency for the threads on the outside of the hank to dry somewhat faster than the threads on the inside of the hank, producing a somewhat.

tangled condition in the han In the preferred practice of our process, the hanks of wet silk are hung in a dryer so arranged that humidity of the atmosphere inside the {drier can be accurately controlled and the silk is slowly dried to a moisture content of 30 to 40 per .cent. At this point, the silk is removed, wound onto rolls or reelsand returned to the drier where it is dried to a moisture content of 7 per cent. Dryin in this manner allows the silk to effect its nal drying under sufiicient tension to bring out a high lustre, somewhat better than when it is dried directly to 7 per cent with no tension. While the tension produced on the silk fibres during drying from 30 to 40 per cent moisture to 7 per cent moisture'is sufiicient to develop the full lustre of the artificial silk, this tension is insufficient to cause breaks in the fibres and, in addition, is so low that the finished sllk is soft and strong. v

The hanks of. silkare removed from the drier, slipped onto reels and may be either rewound into hanks of any desired length orwound directly onto spools ready for use.

While We have described in detail the preferred practice of our process, it is to be un-* derstood that the details of procedure may be Widely varied without departing from the spirit of the invention or the scope of the subjoined claims. k We claim: v

31. In the herein described process of manufacturing artificial silk and the like, the steps of washing freshly spun cuprammonium silk filamentsto remove excess alkali therefrom, twisting said filaments while in wet condition, further washing said filaments without tension, removing a major portion of the moisture content of said filaments without said filaments without tension thereon to from approximately 30 to 40 per cent moisture, and thereafter further drying said fila- 'ments'under tension.

In testimony whereof, we aifix our signatures.

HARRY P. BASSETT. THOMAS F. BANIGAN. 

